The application of various types of torque motors to control a throttle or valving element in the air intake passage of an internal combustion engine is well known. More recently, so called "fly-by-wire" systems have been proposed which totally eliminate mechanical linkage between the operator's accelerator pedal and the engine throttle body, providing, in its place, a torque motor which operates to position a throttle valve shaft in response to an electrical operator demand signal.
Such arrangements typically employ a motor and throttle valve as separate elements, wherein an output shaft of the motor is connected to a throttle valve through a coupling, and wherein the degree of opening of the throttle valve is modulated in accordance with rotational displacement of the output shaft of the motor. Such arrangements have not received wide commercial acceptance, however. The provision of structure between the motor and throttle body tends to proliferate part count and unit cost as well as requires a large space in the engine compartment of the host vehicle. Additionally, the use of separate motor/throttle valve structures raise the possibility of certain failure modes in which torque transmission from the output shaft fails to appropriately position the throttle valve shaft such as through binding and the like.
The above described shortcomings of the prior art have been, in part, recognized and apparatus suggested incorporating a motor rotor and throttle valve plate mounted on a common shaft. Such an arrangement is described in U.S. Pat. No. 4,601,271 to Ejiri et al. Such structure provides for simplified design, reduced part count and compact packaging of a single integrated device.
The application of such devices as a prime throttle control for an internal combustion engine of an automobile requires a high degree of reliability and responsiveness to varying operator and system input signals. Accordingly, the motor must be sized to provide extremely fast response to input signal changes over a sustained period of time and in an extremely hostile environment involving large temperature gradients, contamination and corrosive atmosphere. Although, the motor must have substantial electromagnetic "muscle" to provide appropriate response time, mass of the rotating elements must be held to a minimum to prevent inertia induced overshoot requiring damping or other response degrading add-ons to the design.
One way to effect enhanced motor response while minimizing mass of rotating elements is to reduce the working gaps in the magnetic circuit of the motor. This is accomplished through precision manufacturing techniques not generally employed in the automotive industry. Furthermore, the integration of a motor and throttle body in a single assembly can cause additional tolerance stack up as well as reduced reliability and unit to unit repeatability. Finally, integrated designs such as described in U.S. Pat. No. 4,601,271 make post assembly calibration of the various operating elements difficult and commercially unfeasible.
It will be apparent from a reading of the specification that the present invention may be advantageously utilized with various types of associated loads for may different application. However, the invention is especially useful when used in combination with a throttle body for controlling the air inlet passage to an internal combustion engine, and will be described in connection therewith.